In the field of non-impact printing, the most common types of printers have been the thermal printer and the ink jet printer. When the performance of a non-impact printer is compared with that of an impact printer, one of the problems in the non-impact machine has been the control of the printing operation. As is wellknown, the impact operation depends upon the movement of impact members, such as print hammers or wires or the like, which are typically moved by means of an electromechanical system and which may, in certain applications, enable a more precise control of the impact members.
The advent of non-impact printing, as in the case of thermal printing, brought out the fact that the heating cycle must be controlled in a manner to obtain maximum repeated operations. Likewise, the control of ink jet printing, in at least one form thereof, must deal with rapid starting and stopping movement of the ink fluid from a supply of the fluid. In each case of non-impact printing, the precise control of the thermal elements and of the ink droplets is necessary to provide for both correct and high-speed printing.
In the matter of ink jet printing, it is extremely important that the control of the ink droplets be both precise and accurate from the time of formation of the droplets to depositing of such droplets on paper or like record media and to make certain that a clean printed character results from the ink droplets. While the method of printing with ink droplets may be performed in either a continuous manner or in a demand pulse manner, the latter type method and operation is disclosed and is preferred in the present application when applying the features of the present invention. The drive means for the ink droplets is generally in the form of a well-known crystal or piezoelectric type element to provide the high-speed operation for ejecting the ink through the nozzle, while allowing time between droplets for proper operation. The ink nozzle construction must be of a nature to permit fast and clean ejection of ink droplets from the print head.
In the ink jet printer, the print head structure may be a multiple nozzle type with the nozzles aligned in a vertical line and supported on a print head carriage which is caused to be moved or driven in a horizontal direction for printing in line manner.
Alternatively, the printer structure may include a plurality of equally-spaced horizontally-aligned single nozzle print heads which are caused to be moved in back-and-forth manner to print successive lines of dots in making up the lines of characters. In this latter arrangement, the drive elements or transducers are individually supported along a line of printing.
In a still different structure, the nozzles are spaced in both horizontal and vertical directions, and the vertical distance between centers of the ink jets equals the desired vertical distance between one dot and the next adjacent dot above or below the one dot on the paper. The horizontal distance is chosen to be as small as mechanically convenient without causing interference between the actuators, reservoirs, and feed tubes associated with the individual jets. The axes of all jets are aligned approximately parallel to each other and approximately perpendicular to the paper. Thus, if all nozzles were simultaneously actuated, a sloped or slanted row of dots would appear on the paper and show the dots spaced both horizontally and vertically. In order to produce a useful result consisting of dots arranged as characters, it is necessary to sweep the ink jet head array back and forth across the paper, and actuate each individual nozzle separately when it is properly located to lay down a dot in the desired position. A vertical row of dots is created by sequentially actuated the nozzles rather than simultaneous actuation, the latter being the preferred practice in the more common nozzle arrangements.
A further observation in ink jet printers is that previous and current designs for drop-on-demand ink jet print heads are sensitive to the ingestion of air into or the presence of air in the supply of ink. Even a small air bubble can interrupt or fault the performance of transducers or like devices that expel ink droplets from a nozzle by means of pressure pulses created within an ink-filled chamber or channel.
The use of a fast-action valve or like device to control the flow of ink to a single ink jet printing nozzle is known in specific applications, but in certain cases, the concept and heretofore-known structure has been considered costly and impractical. Additionally, the supply of ink to a plurality of ink jet nozzles may be controlled by means of a single control device wherein the nozzles are connected to a common manifold and ink droplet ejection is accomplished by momentarily increasing the pressure in the manifold.
After the droplets of ink have been ejected from the nozzles, the ink is replenished thereat from a remote supply by the capillary action of the meniscus at the end of the nozzle. In certain of the control devices and arrangements, it has been found that some difficulties arise from the capillary action refill or replenish process and there are adverse effects on the performance and reliability of such printers.
In normal operation of an ink jet print head, it is well-known that a negative meniscus of ink should be maintained at the nozzle, that the relative levels of ink in the various parts or areas of the system have an effect on the printing operation, and further, that the movement of the several printer elements affects the flow of ink during the printing cycle.
Representative documentation in the field of ink control means for ink jet printers includes U.S. Pat. No. 3,737,914, issued to C. H. Hertz on June 5, 1973, which discloses a liquid jet recording system in which an electrically-conductive fluid is pressure-ejected through capillary nozzles to form jets directed toward a recording sheet and wherein a group of the jet nozzles are mounted in a common plane and are movable periodically in side-to-side direction.
U.S. Pat. No. 4,042,937, issued to F. J. Perry et al. on Aug. 16, 1977, discloses an ink supply system for an ink jet head which includes an inlet valve connecting a pump in the line from a reservoir to the head and an outlet valve connecting an outlet from the head to the reservoir. At time of shut off, the inlet valve is closed with the outlet valve open to create a negative pressure in the head.
U.S. Pat. No. 4,079,384, issued to R. Takano et al. on Mar. 14, 1978, discloses an ink liquid supply system having an ink cartridge, an ink reservoir, a pump and a cross valve in the supply line.
U.S. Pat. No. 4,153,902, issued to Y. Kanayama on May 8, 1979, discloses an ink liquid supply system wherein a subtank is interposed between an ink reservoir and a pump in the supply line. A valve and a pair of filters are also provided in the line.